Preheat oven to 350° F.
Parboil peppers in boiling water 5 minutes and drain.
In a medium bowl, thoroughly mix onion, rice, ham, cayenne if desired, and 1/2 cup cheese.
Stuff pepper shells generously with rice mixture and top with additional cheese.
Bake at 350° F for 40 minutes, or until cheese is melted and browned.